Two metal-filled epoxy products can list nearly identical headline numbers — the same Tg, the same lap shear figure, the same continuous-service temperature — and still perform completely differently in the same repair, because a data sheet number only means what its test method and test conditions say it means, and those details rarely make it into the marketing summary.

Why a Single Tg Number Rarely Tells the Whole Story

Glass transition temperature can be measured several different ways, and each method tends to produce a somewhat different number for the identical cured material — a DMA-derived Tg using the peak of the tan delta curve, a DSC midpoint measurement, and an onset-of-softening figure can all differ by a meaningful margin on the same sample. A data sheet that reports a single Tg figure without specifying the test method leaves an engineer unable to compare it fairly against a competing product tested by a different method, even when both figures look similarly impressive. Before treating a Tg number as the deciding factor between two products, confirming both were measured the same way is a step worth the extra phone call.

Lap Shear Numbers Depend on Substrate Prep as Much as Chemistry

A published lap shear strength is only as meaningful as the surface condition it was tested on, and this is one of the most commonly overlooked details in a head-to-head product comparison. The identical epoxy chemistry tested on a grit-blasted steel coupon versus a solvent-wiped-only coupon can show a shear-strength difference large enough to change which product looks “stronger” on paper, even though the underlying chemistry never changed — only the surface preparation used to generate the number did. A data sheet’s shear strength figure, without a stated surface preparation standard, tells you what the chemistry is capable of under laboratory-ideal conditions, not necessarily what a field repair with more modest surface prep will actually achieve.

Continuous vs. Intermittent Rating: A Distinction Worth Confirming Directly

A headline temperature rating on a data sheet is frequently an intermittent or peak exposure figure rather than the continuous-service number that should actually drive a specification for equipment running at sustained temperature. Applying a product rated for a brief intermittent excursion to 300°C as though that figure represented safe continuous duty is a common and avoidable misreading — the continuous-service rating for the same product is often meaningfully lower, since sustained thermo-oxidative exposure degrades a polymer matrix differently than a short peak exposure does. Confirming which figure applies to the actual duty cycle of the repair, rather than assuming the more impressive number on the page is the relevant one, is a five-minute check that prevents a specification error with real consequences.

What to Request Beyond the Standard Published Data Sheet

A few additional pieces of documentation, not always included in a standard published data sheet, are worth requesting before committing a high-value or safety-relevant repair to a specific product:

• Test substrate and surface preparation standard used to generate the published shear strength figures, so the number can be compared against the repair’s actual expected surface condition.
• Thermal-cycling fatigue data, not just static strength at temperature — a bond that holds under a single elevated-temperature pull test can still develop fatigue cracks after repeated thermal cycling that a static test never reveals, a distinction covered further in how CTE mismatch causes adhesive bond failure.
• The exact post-cure schedule used to generate the published Tg and strength figures — a product tested only after a specified post-cure bake will underperform its published numbers if applied in the field with a room-temperature cure alone and no post-cure step.
• Whether the continuous-service temperature figure has itself been validated by long-term aging data, or is simply an extrapolation from shorter-duration testing.

Incure documents test substrate, surface preparation standard, and post-cure schedule alongside its published Tg and shear strength figures specifically so a specifying engineer isn’t left guessing which conditions produced the numbers on the sheet. Email Us with a competing data sheet you’re evaluating against an Incure Epo-Weld formulation, and the technical team can walk through what each figure actually represents before you commit to a specification.

Frequently Asked Questions

Q: Is it reasonable to assume two products with identical published Tg figures will perform identically in the same repair?
A: Not necessarily — if the test methods or post-cure schedules used to generate those figures differ, the identical headline number can represent meaningfully different real-world performance once the surface preparation and duty cycle of the actual repair are factored in.

Q: Does requesting this additional documentation typically slow down a repair timeline?
A: For a routine, low-consequence repair, usually not enough to matter — but for a safety-relevant or high-value asset, the time spent confirming test conditions is small compared to the cost of a repair that fails once the actual duty cycle differs from what the published figures assumed.

Reading past the headline numbers on a high-temperature metal epoxy data sheet — checking test method, surface prep, post-cure schedule, and whether a temperature rating is continuous or intermittent — is what separates a specification built on real comparable data from one built on marketing summaries that happen to look similar. For a broader look at product selection criteria and Incure’s consultative specification process for this category, see Incure’s guide to high temperature metal epoxy, and for how metal-filled epoxy bond strength compares against other adhesive chemistries in heavy-duty repair work, see which is stronger for heavy-duty repairs, UV glue or epoxy. Contact Our Team to review a specific data sheet comparison before finalizing a repair specification.

Visit www.incurelab.com for more information.